Photovoltaic devices that use Cu(In, Ga)Se2 (CIGS) as an absorber layer have improved in recent years, and have the potential to achieve even higher efficiencies. One related art method of forming CIGS films involves sputtering metals from Cu, Ga, and In targets, and converting these precursors into CIGS films by reacting them with Se vapor or H2Se/H2S. However, as shown in FIG. 1, this method produces a CIGS absorber layer with a steep Ga gradient having low levels of Ga at the front of the CIGS absorber layer, which causes a low bandgap and a low open-circuit voltage (Voc). Further, as shown by the cross-sectional scanning electron microscopy (SEM) image of the CIGS absorber layer in FIG. 2, this absorber layer suffers from a poor microstructure having voids, as well as problematic back contacts. Despite efforts to homogenize the Ga distribution within the absorber layer, the efficiency of the resulting photovoltaic devices incorporating these CIGS films remains low.